Threatened freshwater fishes of Great Britain

Abstract

Recent glaciation has resulted in temperate fish communities being much less diverse than those of the tropics and in Great Britain there is a marked reduction in specics from south to north. Of the 56 species on the British list, 15 are introduced and 41 are native species. Nine of the latter are regarded as being significantly threatened and in need of conservation protection and management. Five of these fish are anadromous species. The sturgeon Acipenser sturio, is a vagrant around British coasts and is now rare. Allis shad Alosa alosa is also very rare and there are no known spawning sites in Great Britain; the twaite shad Alosa fallax is declining too with only a few known spawning sites. The houting Coregonus oxyrhynchus, now extinct in Great Britain, formerly occurred off the south east coast. Finally, the smelt Osmerus eperlanus is in serious decline in many areas. For example, in Scotland, only three populations remain of at least eleven known to occur at the beginning of this century. The other four threatened fish are purely freshwater species. The Arctic charr Salvelinus alpinus has a decreasing number of populations - though Scotland remains a stronghold. The powan Coregonus lavaretus is found in only seven waters - two in Scotland, four in England and one in Wales. The vendace Coregonus albula, now extinct in Scotland, occurs in only two lakes in England. Finally, the burbot Lota lota is now extinct in Great Britain. It formerly occurred in low-lying rivers on the east coast of England, but no specimens have been seen since about 1970. In addition to these rare fish, there are several distinct stocks of common native specics with unusual characteristics which are worthy of special conservative measurements. These fish include a purely freshwater race of the normally anadromous river lamprey Lampetra fluviatilis in Loch Lomond, a dwarf form of brook lamprey, Lampetra planeri in the Inner Hebrides, spineless three-spined sticklebacks Gasterosteus aculeatus in the Outer Hebrides and several distinct races of brown trout Salmo trutta; and perhaps other species. There are also valuable fish communities in individual waters which merit conservation attention. These are important for a variety of reasons, including high (and very low) natural diversity, unique assemblages, pristine stocks and highly characteristic communities. For example, the fish community in Loch Eck has a unique combination of species which includes Atlantic salmon Salmo salar, brown trout, Arctic charr and powan - these species are not found together anywhere else in Great Britain.